The present invention relates to fasteners for supporting and aligning a connecting flange on a transmitter body before permanent fasteners are installed. The flange is retained by the supporting and aligning fasteners in an unsealed condition so that if fluid pressure is supplied to the flange prior to installation of permanent fasteners, the fluid will leak freely and not build up pressure, which could result in sudden release. The invention also relates to providing permanent fastener bolts that are threadable into provided threads on the body only when the proper length bolt is used to insure full required thread engagement.
In the use of process control pressure transmitters, which include pressure sensor bodies having internal pressure sensors, several different adapters for connecting the fluid pressure piping from a process line to the pressure body are required for accommodating various pressure connections and user requirements in individual process equipment. For example, it is normal to provide a standard coplanar flange with one-quarter inch pipe tap connections installed at the factory with suitable permanent fasteners. One-half inch pipe thread mounting adapters that can be put on in the field are available. A standard coplanar flange also can be used with a three-valve manifold, and flange adapters are then also needed on the input side of the manifold. The thickness of the bolt receiving parts that are mounted to the transmitter body differs in each of these configurations, and thus each configuration requires a different length of permanent mounting bolt. In order to standardize shipments, three different sets of mounting bolts are shipped with each transmitter, including the standard set installed to hold the coplanar flange by itself.
The coplanar flange is also mounted by two alignment or temporary mounting screws, so if the permanent fastener bolts are removed for any reason, including change of input configuration, the coplanar flange remains supported and aligned in place on the transmitter. The alignment screws are to be used only for aligning and temporarily supporting the flange and body together if changes in the flange configuration are made. When the coplanar flange is mounted at the factory directly to the sensor body, short (first) permanent mounting bolts are used. If one-half inch pipe adapters are added to the flange, the first bolts have to be removed, and longer bolts which pass through the adapters and the flange installed. The three-valve manifold also mounted on the flange requires longer than standard bolts. If the installer does not install the longer permanent mounting bolts when changing input configuration and applies pressure, the alignment screws used on previous transmitters can fail. Also, if there is an attempt to install shorter bolts where longer ones are needed (if the installer is totally inattentive), the prior shorter bolts may be slightly engaged in the threads of the transmitter body. The alignment screws that are holding the flange in place do not have sufficient strength to hold the flange against pressure loads. The threads of the erroneously installed main mounting bolts may strip, and the alignment screws will fail, resulting in damaging the transmitter.